Patterning domains in the vertebrate mesoderm

In vertebrates, the postcranial musculoskeletal system is formed from two distinct mesodermal populations, the somites and lateral plate. Axial skeletal elements such as the vertebrae and ribs arise from somitic mesoderm, whereas skeletal elements of the limbs derive from lateral plate mesoderm. Notably, all musculature originates from the somites, but the embryonic context of myoblast differentiation varies with body region. Most axial muscles, such as the deep muscles of the back, form from somitic cells that differentiate in an entirely somitic environment. These muscles are primaxial. In contrast, limb muscles form from somitic cells that leave their parent somites and mix with lateral plate derived mesenchyme. Since these muscles differentiate in a lateral plate environment, they are abaxial.

The interface between the primaxial and abaxial domains is the lateral somitic frontier.

Our current research seeks to explore the dynamics of the lateral somitic frontier during ontogeny, and to place these observations in a comparative context to make inferences about the evolution of the vertebrate musculoskeletal system. We hypothesize that the primaxial and abaxial domains are patterned independently during development and that somitic cells crossing the frontier become re-patterned by their new environment. We also hypothesize that the developmental modularity of the primaxial and abaxial domains facilitates evolutionary change across taxa. (contributed by Swetha Mummini’14)